The present invention is directed to an improvement in the type of hermetically sealed electrical terminal taught in U.S. Pat. No. 3,770,878, issued Nov. 6, 1973 and entitled "Hermetically Sealed Electrical Terminal". In accordance with this patent, one or more highly conductive conductor pins formed from materials, such as copper and copper alloys, are electrically insulated from a supporting member, such as a ferrous metal shell, by means of a molded dielectric sealing member which coacts with the conductor pins and the supporting member to provide a hermetically sealed terminal. Such terminals are widely used in refrigeration headers wherein an electrical connection is made with components mounted within a sealed receptacle or chamber containing fluid, either liquid or gaseous, which is under pressure. An essential prerequisite of such terminals is the provision of a seal which is capable of maintaining a tight bond with both the conductor pins and the supporting body irrespective of environmental conditions, such as elevated temperatures or testing procedures which may act to interfere with the effectiveness of the seal by providing leakage paths which will permit fluid to escape through the header.
While electrical terminals of the type taught in the aforementioned patent have proven to be highly successful in applications wherein temperatures of up to 400.degree. F. are encountered, it has been found that leakage can occur where temperatures in excess of 400.degree. F. are encountered, and it has been a desire in the industry to provide terminals which remain reliably sealed to temperatures up to 500.degree. F.
Another source of potential leakage results from testing procedures utilized to test the integrity of conductor tabs which may be welded to either or both ends of the conductor pins to facilitate the attachment of conductive wiring to the pins. A conventional test is to apply a twisting or torque force to the tabs to be certain they are tightly bonded to the pins. Such forces are transmitted to the pins and even a very slight movement of the pins relative to the sealing material will result in the formation of a leakage path along the interface of the pin with the seal. While terminal pins have heretofore been provided with a centrally disposed knurl to inhibit rotation of the pins, such arrangement will not ensure against leakage along the pin if both ends of the pin are provided with conductor tabs and subjected to torque forces.
The present invention provides an improved terminal construction which effectively prevents the formation of leakage paths between the sealing member and the supporting body and also between the sealing member and the terminal pins. This new construction is temperature stable and provides reliability under higher temperatures than terminals currently in use.
FIG. 1 illustrates a prior art hermetically sealed terminal of the type disclosed in U.S. Pat. No. 3,770,878. As seen therein, the terminal comprises a supporting member or body 1 which is the type used in compressors for refrigeration equipment, the body being of cup-shaped configuration and having an annular body wall 2 terminating at one end in an outturned mounting flange 3 and at its opposite end in a base 4 interrupted by spaced apart sleeves or sockets 5 lying within the confines of the annular body wall 2. The supporting member 1 mounts conductor pins 6 which extend axially through the sleeves 5, the conductor pins being secured in place and hermetically sealed by means of a sealing member 7, which is preferably a unitary member composed of a dielectric material molded in situ to the desired configuration.
In the event excessive temperatures are encountered which cause differential expansion of the parts or creeping of the sealing member relative to the surfaces of the supporting member, leakage paths may develope between the points 8 and 9, such leakage paths being diagrammatically indicated by the dotted line 10. As will be evident, such path is relatively short and basically involves the flow of fluid around the inner and outer surfaces of the sleeve 5.
If the terminal pins 6 are provided with conductor tabs 11, similar leakage paths may be formed between the pins 6 and the sealing member 7 as an incident of testing the integrity of the attachment of the conductor tabs to the pins. When torque forces are applied, the pins will tend to rotate relative to the sealing member and even an extremely small movement may break the bond between the pins and the sealing member. While in the embodiment illustrated, the terminal pin is provided with a knurl 12 located within the confines of the sleeve 5 to prevent rotation of the pin, the position of the knurl is such that it does not effectively prevent the formation of leakage paths 13 and 14. If only the outer ends of the pins are provided with conductor tabs, the leakage path 13 alone is normally insufficient to pose a problem; however, if the inner ends of the terminal pins are also provided with conductor tabs, the presence of both leakage paths 13 and 14 can pose a problem in that the application of torque to both ends of the pins may result in a loss of integrity of the sealing member in the area of the knurl, thereby permitting fluid under pressure to escape.